1. Field of the Invention
The present invention relates generally to methods of measuring levels of liquids, and more particularly is method utilizing an automatic dual-phase instrument for continuously monitoring a dual-phase reservoir.
2. Description of the Prior Art
Currently, only manual measuring techniques are commonly used to measure liquid levels in a reservoir containing at least two immiscible liquids, such as in environmental monitoring wells. In environmental monitoring wells, it is desirable to measure the thickness of a free-product (product) layer, the depth-to-product (dtp), and the depth-to-groundwater (dtw). The measurements are most typically performed using a manual interface probe. The interface probe consists of a sensor attached to a signal/support cable (which is typically marked in graduations of 0.01 feet) that is wound around a hand reel. The sensor is capable of differentiating between the free-product and groundwater. As the sensor passes into and through each layer of liquid, the interface probe signals the operator audibly and/or visually. The interface probe signal differs depending on whether the sensor is detecting air, product, or water. The operator notes the dtp and dtw by checking the amount of cable that has been unrolled when the instrument indicates that the sensor has passed through the air/product interface and the product/groundwater interface. The operator can then easily calculate the thickness of the free-product layer. While fairly accurate, manually taking the measurements does not provide continuous monitoring, and is time consuming and tedious.
There are many devices disclosed in the prior art that measure, monitor, and control single phase liquids. One such measuring device is the “Fluid Level Monitor” of Yekutiely, et al., U.S. Patent Application # 20020029633, published Mar. 14, 2002. This device is able to monitor depth of a liquid by measuring the tensile force in a filament and a rotation of a spool around which the filament is wound.
The “Digital Electronic Liquid Density/Liquid Level Meter” of Articolo, George A., U.S. Patent Application # 20010029782, published Oct. 18, 2001, discloses a device that requires only a single float to directly and continuously measure a liquid level. The Articolo device can be used to determine specific gravity if two floats are used together.
The “Method and Apparatus for Controlling the Level of Liquids” by Molina, et al., U.S. Patent Application # 20030131661, published Jul. 17, 2003, discloses a method of accurately monitoring the level of a liquid in a container by correcting for the variation of the specific gravity values with temperature.
“Liquid Level Detection” by Fryer, et al., U.S. Pat. No. 5,094,102, issued Mar. 10, 1992, teaches a method and apparatus to monitor a liquid level in a bore hole and to activate a signal when the level reaches a monitor point.
The “Liquid Level Detector” of Toon, et al. U.S. Pat. No. 4,989,452, issued Feb. 5, 1991, discloses a probe that is lowered into a water well of other vessel and uses conductivity measuring electrodes to distinguish between the phases of liquid in the well. The device has an optical sensing facility to locate the top level of the liquid phase.
Finally, there are also some references directed to measuring the levels in a dual-phase vessel. One such reference is the “Method of Accurately Gauging Groundwater and Nonaqueous Phase Liquid Contaminants which Eliminates Cross Contamination Between Wells” by Milone, Christopher J., U.S. Patent Application # 20030041662, published Mar. 6, 2003. This method teaches the use of a dedicated detector (a conductive and hydrostatic resistive circuit) formed on a thin-film tape affixed to the wall of a well casing. The use of a dedicated detector does avoid cross contamination from the probe, however, the affixing of the detector at a given location limits the versatility of the device. This drawback is particularly limiting in applications in which multiple locations need to be tested, such as in field pilot-testing. Moreover, the inability to remove the device from the well makes service on the device difficult if not impossible.
Another dual-phase measuring device is the “Level Sensor” of Zinsmeyer, et al., U.S. Pat. No. 3,935,741, issued Feb. 3, 1976. The Zinsmeyer device uses a pair of magnets mounted in floats, each float being calibrated (by selecting the density of the material of the float) to float on one of two immiscible liquids. The floats are joined by a mechanical linkage, and as the liquid levels change the floats move coded tapes which are monitored by an optical reader. While this method is useful for measurements taken in tanks, the mechanical linkage of the two floats makes the system impractical for deep-well applications. The requirement for an optical reader also makes the Zinsmeyer method difficult to implement for in-well or on-well applications.
Accordingly, it is an object of the present invention to provide a removable and serviceable device to continuously measure the levels of dual-phase liquids.
It is another object of the present invention to provide a device that can be used in deep-well and small diameter well applications.